Old clay tile and concrete beam floor cracks

[haynewp]

We have a floor that experienced the attached cracks. It is a 100 year old clay tile system where they used 8" tile and 2" of topping which created the 10" total depth concrete T-beams as shown on the joist load table diagram on the attached file. The T-beams are spaced at 17" on center and are about 5 inches thick at the bottom. The T-beams have the attached reinforcing at the bottom and top at the ends on the attached original drawing I recently found.

The bottom of the floor did not show any damage from overloading in any areas, only some rust damage. They drilled a couple of locations in the top of the slab and the cracks went an inch or a slightly more deep, but I can't say for sure the cracks don't extend down below the topping and into the beams at some locations. The cracks are not something that have been there for years. These appear to be yield line type cracks but the pattern does not meet what I would have expected for a one-way slab, unless the top temperature bars altered the yield lines? Also, there was no spalling off of the top concrete from compression that I am aware of and none of the bottom of the beams were cracked. There is an adjacent existing room that have similar but old topping cracks that have been worn down from rolling cart traffic. Any thoughts on the attached crack patterns?

 

[haynewp]

The attached was also in the incomplete existing drawing set, but I believe it was either meant to apply typically to another area or is incorrectly shown since the temperature bars should be up in the topping and not down running into the adjacent clay tiles.

 

[phamENG]

The column grid looks pretty square. It may have been designed as a 1-way slab, but the geometry may be forcing it to act more like a 2-way slab despite the light reinforcing in the transverse direction.

Am I correct in assuming the second picture (with 3 cracks coming together) is in the corner bay? May be a trick of the lighting, but it looks like you have a relative vertical displacement across the crack, which could suggest cracking caused by upward deflection due to a (very) imbalanced load across the bays. It does look surprisingly like a yield line failure analysis model.

 

[haynewp]

I unfortunately did not take these pictures and can't say for sure, they were taken during the repair process but I believe you are correct. Here is another one where you see the cracks have extended further than the cracks that were drawn on the previous attached diagram months ago.

That was my idea as well, the topping slab and temperature reinforcing creating two-way slab behavior in the transverse direction to the T-beams.